Morbo refers to himself as 'the Annihilator' and frequently threatens mankind.
Has he or his species ever made good on his threats? Or is Linda right in dismissing him?
Morbo's comments seem to be a setup to a plot that has not happened yet. Whether the writers want Morbo's people to attack the Earth or whether it is just a joke and his threats should not be taken seriously is completely up to them. My fingers are crossed that something has happened to his people and he does not know it yet.